Efficient and stable coupling to nanophotonic waveguides and resonators in stringent environments.

Using conical optical fibers, we explore new methods for coupling light to nanophotonic structures operated in constrained environments. With a single-sided conical fiber taper, we demonstrate efficient coupling to an on-chip nanophotonic bus waveguide immersed in a liquid. In the aim of coupling light into a target whispering gallery disk resonator, we then replace such on-chip nanophotonic bus waveguide with two conical fibers joined face to face. This latter approach leads to highly efficient coupling superior to 90% and is shown to be stable within a vibrating pulse tube cryostat operating at low temperatures. It is demonstrated in the telecom band and in the near infrared close to 900 nm of wavelength. Conical fiber methods hence enable reaching the coupling performances required in quantum optics or sensing experiments, even in stringent environments where signal-to-noise had remained a challenge.